In the fields of explosion protection flameproof enclosures (Ex-d) represents one type of protection. It is based on enclosing electrical operating means, which can be sources for a spark, such that explosions which occur in the housing interior do not result in flames, hot particles or gases that reach and ignite the outside atmosphere. In such flameproof enclosures, temperatures at locations on the protective housing above the ignition temperature of ignitable gases or dust are furthermore avoided. Overpressure, which is created in the protective housing due to an explosion, with regard to the surrounding area of the housing, also must be reduced safely by compensating with the surrounding area. For cooling the hot gases and for extinguishing potential sparks, provision is thus made for a gas-permeable flameproof passage between the interior of the protective housing and the surrounding area of the protective housing.
DE 10 2010 016 782 A1 describes a pressure release device comprising a porous body, which is arranged in an accommodating body. In its edge area, the porous body comprises a pore closure. The pore closure on the edge side is to prevent the porous body from being bypassed by a flame or hot gases. To embody the pore closure, the publication proposes, for example, to pretension the porous body at its edge against a conical seat of the accommodating body. For this purpose, the publication shows an exemplary embodiment comprising a tire-like body made of soft metal, which is arranged around the porous body and which encloses the latter on the edge side. The accommodating body comprises an internal thread, in which a clamping nut is inserted, with the help of which the force, which is required for forming the preliminary tension, is exerted on the edge area of the porous body. A different example shows an accommodating body comprising an internal thread and a clamping nut, which squeezes the porous material of the porous body on the edge side so that the pores of the porous body collapse. The mentioned embodiments have the disadvantage that the introduction of a thread and of a clamping nut and the closing of the pores of the porous body on the edge side leads to the reduction of the effective cross section for the pressure release device. However, a cross section, which is as large as possible is desired in terms of an effective pressure release. To some extent, the mentioned pressure release device requires extensive production of the porous body and of the accommodating body so as to create the ability to be flameproof, in that the circulation of the porous body is prevented by means of pore closure.